[WIP] use marker trait + refactor inmemory layer

[yliang412]

Problem

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

5013 tests run: 4854 passed, 1 failed, 158 skipped (full report)

---

Failures on Postgres 17

• test_subscriber_restart: debug-x86-64

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_subscriber_restart[debug-pg17]"

Flaky tests (15)

Postgres 17

• test_pageserver_compaction_smoke: release-x86-64, release-arm64
• test_sliding_working_set_approximation: debug-x86-64
• test_graceful_cluster_restart: debug-x86-64
• test_subscriber_restart: release-x86-64

Postgres 16

• test_pageserver_compaction_smoke: release-x86-64, release-arm64
• test_ondemand_wal_download_in_replication_slot_funcs: release-x86-64
• test_subscriber_restart: release-x86-64

Postgres 15

• test_pageserver_compaction_smoke: release-x86-64, release-arm64
• test_multi_attach: release-arm64
• test_subscriber_restart: release-x86-64

Postgres 14

• test_pageserver_compaction_smoke: release-x86-64, release-arm64

Test coverage report is not available

_{The comment gets automatically updated with the latest test results
fe99bb9 at 2024-10-04T16:36:44.941Z :recycle:}

[yliang412]

#9693